1. Field of the Invention
This invention relates to high aspect ratio microstructures, and field emission devices using such microstructures as spacers. More particularly, this invention relates to processes for creating support structures that provide support for a flat panel display against the atmospheric pressure on the display screen without impairing the resolution of the display's image.
2. Description of the Related Art
Cathode ray tube (CRT) displays, as used in desk top computer screens, function as a result of a scanning electron beam from an electron gun impinging on a pixel's phosphors of a display screen. The electrons from the beam thus increase the energy level of the pixel's phosphors. When the phosphors return to their normal energy level, the phosphors release photons through the glass screen of the display to the viewer. Flat panel displays (e.g., as seen in U.S. Pat. Nos. 5,410,218, 5,391,259, 5,387,844, 5,374,868, 5,372,901, 5,372,973, 5,358,908, 5,358,601, 5,359,256, 5,357,172, 5,342,477, 5,329,207, 5,259,799, 5,186,670, 5,151,061, 5,070,282, improve on CRTs by combining the cathodoluminescent-phosphor technology of CRTs with integrated circuit technology to create a thin, high resolution display where each pixel has its own electron beam (or emitter). This type of display technology is becoming increasingly important in today's computer industry.
A relatively high voltage differential (e.g., generally above 200 volts) exists between the cathode surface (also known as base electrode, baseplate, emitter surface, cathode electron emitting surface) and the display screen (also known as an anode, cathodoluminescent screen, faceplate, or display electrode). Electrical breakdown between the cathode surface and the display screen must be prevented to maintain operation of the display. At the same time, the narrow spacing between the two is necessary to maintain the desired structural thinness and to obtain high image resolution. Further, the spacing must be uniform for consistent image resolution and brightness to avoid display distortion. Uneven spacing is much more likely to occur, however, due to the high pressure differential that exists between the external atmospheric pressure and the pressure within the evacuated chamber between the cathode surface and the display screen.
Support structures (or spacers) placed between the cathode surface and the display screen prevent uneven spacing by maintaining the required constant spacing. To be effective, the support structures must meet the following requirements: (1) be sufficiently non-conductive to prevent electrical breakdown between the cathode surface and the display screen, in spite of the close spacing (on the order of 100 microns) and relatively high voltage differential (200V or more), (2) exhibit mechanical strength such that they exhibit only slow deformation over time, providing the flat panel display with an appreciable useful life, (3) exhibit stability under electron bombardment, since electrons will be generated at each of the pixels, (4) be capable of withstanding "bakeout" temperatures of around 400.degree. C., necessary to create the high vacuum between the cathode surface and backplate of the display screen, and (5) be small enough in size so as to not to visibly interfere with display operation.
There exist various processes for avoiding the pressure problems mentioned above, such as, for example the following U.S. patents, all of which are incorporated herein by reference:
U.S. Pat. No. 5,247,133 entitled "High-Vacuum Substrate Enclosure" PA1 U.S. Pat. No. 5,205,790 entitled "Method to Form High Aspect Ratio Supports (Spacers) for Field Emission Display Using Micro-Saw Technology" PA1 U.S. Pat. No. 5,342,737 entitled "High Aspect Ratio Metal Microstructures and Method for Preparing the Same" PA1 U.S. Pat. No. 5,232,549 entitled "Spacers for Field Emission Display Fabricated via Self-Aligned High Energy Ablation" PA1 U.S. Pat. No. 4,923,421, entitled "Method for Providing Polyamide Spacers In a Field Emission Panel Display"
There are several drawbacks to the spacers and methods described in the above cited patents. One disadvantage is that the cost of manufacturing is relatively high when compared to using a photolithographic process as in the present invention.